Semiconductor device containing stacked semiconductor chips and manufacturing method thereof

ABSTRACT

An adhesive film is formed on an electrode film, and a coating film is formed thereon. Nickel, chrome, molybdenum, tungsten, aluminum or an alloy of them is used as a constituent material of the adhesive film. Gold, silver, platinum or an alloy of them is used as a constituent material of the coating film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor device provided withsemiconductor chips, and a manufacturing method thereof.

2. Description of the Related Art

Portable electronics devices such as a cellular phone, a PDA, a DVC anda DSC become increasingly sophisticated. The fabrication of the deviceswith a compact size and lightweight are indispensable so that suchdevices are accepted in the market. System LSI higher integrated isrequired for the realization of such devices. On the other hand, LSIused for the devices is required to be with a high functionality and ahigh performance for the realization of friendly and convenientelectronics devices. For this reason, while the number of I/O is.increasing with the acceleration of LSI chip integration, downsizing ofthe package is also required. The development of the packagesappropriate to the board assembly of semiconductor components with ahigh density is strongly desired to satisfy both of the integration andthe downsizing. Some kinds of package technique called CSP (Chip SizePackage) are developed to correspond with such demand.

BGA (Ball Grid Array) is known as an example of such a package asdescribed above. BGA is formed by mounting a semiconductor chip on asubstrate for the package, molding it by resin, and forming solder ballsin an array on the backside surface of the substrate as an externalterminal. Since the mounting part of BGA has an area, the downsizing ofthe package becomes easy. Furthermore, a circuit board corresponding toa narrow pitch, and a mounting technique with a high precision becomeunnecessary. Therefore, a total mounting cost can be reduced by usingBGA even when a packaging cost is relatively high.

FIG. 1 is a schematic illustration of such a standard configuration ofBGA as disclosed in Japanese Laid-Open Patent Application H7-183426. BGA100 has a configuration in which the LSI chip 102 is mounted on theadhesion layer 108 formed on the glass epoxy board 106. The LSI chip 102is molded by mold resin. The LSI chip 102 is electrically connected withthe glass epoxy board 106 by the metal wire 104. The solder balls 112are formed in an array arrangement on the backside surface of the glassepoxy board 106. BGA 100 is mounted on a printed circuit board by theintermediary of the solder balls 112.

In such a package, a semiconductor chip is connected with a interconnectlayer by a wire bonding method or a flip chip method. That is, a padelectrode consisting of a metal film is provided on the top of ainterconnect layer, and the pad electrode is connected with a padelectrode of a semiconductor chip by a predetermined conductive membersuch as a gold wire and solder. It becomes important technical problemsto reduce the resistance at the connecting point and to improve theconnection strength stably, to improve a yield rate and elementreliability.

Related Art List

JPA laid open H7-183426

SUMMARY OF THE INVENTION

The resistance and the connection strength at the connecting point arenot obtained enough in some package formation processes. The inventorsof the present invention recognized that defects frequently arose inwire bonding and so on, in particular when a process including plasmatreatment is introduced for the formation of elements on an interconnectlayer.

The present invention is achieved in view of the aforementionedcircumstances and an object thereof is to provide a technique capable ofsuppressing bad connection between a semiconductor chip and aninterconnect layer so that element reliability and a yield rate areimproved.

The inventors of the present invention investigated earnestly the reasonfor inducing the bad connection between a semiconductor chip and aninterconnect layer. As a result, they found that the surface property ofpad electrodes was changed so that the connection strength declines,when a process such as a plasma treatment, which changes a property ofmetal surface, is implemented in an element mounting process on theinterconnect layer. The present invention is achieved based on suchknowledge.

A semiconductor device according to one aspect of the present inventionincludes: a base material; a conductor circuit provided in the basematerial; a dielectric film covering at least a part of the basematerial; a pad electrode provided on a surface of the base material ora surface of the dielectric film and connected with the conductorcircuit; a semiconductor chip formed on the dielectric film, and aconductive member electrically connecting the pad electrode and thesemiconductor chip, wherein the pad electrode includes a electrode filmand a conductive protective film formed on a surface of the electrodefilm, and the conductive member is formed so that one end thereofcontacts with the conductive protective film.

A manufacturing method of a semiconductor device according to one aspectof the present invention includes: providing a base material including aconductor circuit; with forming a dielectric film covering at least apart of the base material, forming a pad electrode, which is connectedwith the conductor circuit, on a surface of the base material or asurface of the dielectric film; and performing plasma treatment ofexposed surfaces of the dielectric film and the pad electrode.

According to the present invention, degradation of surface of padelectrodes can be suppressed since a conductive protective film isprovided on the surface of the pad electrodes.

This semiconductor device may have a construction in which the surfaceof the dielectric film is a plasma treatment surface, and the surface ofthe conductive protective film includes a plasma-resistant material. Thedielectric film may have a cluster of micro projections formed on thesurface thereof by the plasma treatment. Although the plasma treatmentof the surface of the dielectric film leads to the improvement ofadhesion for a film formed thereon, degradation of the surface of thepad electrode simultaneously arises, and the bad connection between thesemiconductor chip and the interconnect layer becomes a problem.According to the construction described above, such a problem can besolved since the degradation of the surface of the pad electrode can besuppressed by the conductive protective film.

The semiconductor device may have a construction in which the dielectricfilm has a concave part, the pad electrode is formed inside the concavepart, and a void part is provided between the inside wall of the concavepart and the side wall of the pad electrode. With this construction, theadhesion for the film, such as mold resin, formed on the dielectric filmcan be improved. Furthermore, the surface of the pad electrode becomesless subject to the attachment of particles of the dielectric filmmaterial.

The conductive protective film according to the present invention mayinclude an adhesive film formed on the electrode film, and a coatingfilm formed on the adhesive film, which constitutes the surface of theconductive protective film.

This summary of the invention does not necessarily describe allnecessary features so that the invention may also be a sub-combinationof these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a package configuration according to a prior art.

FIG. 2 shows a configuration of ISBTM.

FIG. 3A shows manufacturing process of BGA.

FIG. 3B shows manufacturing process of ISBTM.

FIG. 4 shows a configuration of a semiconductor device according to theembodiment.

FIG. 5A shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

FIG. 5B shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

FIG. 5C shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

FIG. 6A shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

FIG. 6B shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

FIG. 7A shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

FIG. 7B shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

FIG. 7C shows a manufacturing process of a semiconductor deviceaccording to the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention will be described below based on the preferredembodiments, the ISB™ configuration introduced in each embodiment willbe now described prior to it. ISB™ (Integrated System in Board) is aunique package developed by the inventors of the present invention. ISB™is a unique coreless system-in package in the packaging techniquesinvolving electric circuits including semiconductor bare chips mainly,and it has interconnect patterns made of copper but no core (basematerial) to support circuit components.

FIG. 2 shows a schematic illustration of an example of ISB™. Although asingle interconnect layer is shown for a simple explanation of theoverall configuration of ISB™, the configuration practically includes aplurality of interconnect layers stacked. This ISB™ has a configurationthat includes the LSI bare chip 201, Tr bare chip 202 and the chip CR203 connected by interconnect lines that include the copper pattern 205.The LSI bare chip 201 is connected with extraction electrodes and theinterconnect lines by the gold wire bonding 204. The ISB™ is mounted ona printed circuit board by the conductive paste 206 formed beneath theLSI bare chip 201. ISB™ is entirely sealed with a resin package 207 madeof epoxy resin and so on. Although the configuration that includes asingle interconnect layer is shown in this figure, a multilayerinterconnect configuration may be also adopted.

FIGS. 3A and 3B show a comparison of manufacturing processes of aconventional CSP and the ISB™ according to one aspect of the presentinvention. FIG. 3A shows a manufacturing process of the conventionalCSP. A frame is firstly formed on a base substrate, and chips aremounted on the element formation areas segmented by the frame. Afterthat, a package made of thermosetting resin is provided for eachelement, and blanking is performed for each element by using a metaldie. In the final blanking process, the mold resin and the basesubstrate are cut simultaneously. Therefore, the roughness of the cutsurface becomes a problem. Furthermore, since a large amount of wastematerial after the blanking process generates, a problem also arisesfrom the viewpoint of environmental burden.

FIG. 3B shows the ISB™ manufacturing process. Frames are firstly formedon a metal foil. Circuit elements such as a LSI are mounted oninterconnect patterns formed in each module formation area. Afterpackaging each module, finished products are obtained by dicing alongscribing areas. Since the metal foil as a base is removed after thepackaging process and before the scribing process, only the resin layeris cut by dicing in the scribing process. Therefore, the roughness ofthe cut surface can be prevented, and the dicing can be performed moreaccurately.

The following advantages are obtained by the technique of ISB™.

-   (i) Transistors, ICs and LSIs can be made smaller and thinner    because of the coreless assembly.-   (ii) High-performance SIP (System-in Package) can be realized since    a circuit including transistors, system LSIs, chip capacitors and    chip resistors can be formed and packaged.-   (iii) It becomes possible to develop a system LSI in a short term    since existing semiconductor chips can be used in combination.-   (iv) High rate of heat radiation can be obtained since the    semiconductor bare chip is directly mounted on copper.-   (v) Since the interconnect material is copper and there is no core    material, the circuit interconnect has a low dielectric constant so    that the excellent properties in high-speed transfer of data and in    a high-frequency circuit can be obtained.-   (vi) The formation of particle contamination of the electrode    material can be suppressed because of the configuration where the    electrodes are embedded in the package.-   (vii) Environmental burden can be reduced since the package size is    free, and the amount of the waste material per one package is    one-tenth of that of SQEP package having 64 pins.-   (viii) The concept of a system construction can be changed from a    printed circuit board to mount components into a functional circuit    board.-   (ix) The design of ISP patterns is as easy as the design of printed    circuit board patterns, and can be performed by engineers themselves    in set manufacturers.

Next, the preferred embodiments of the present invention will beexplained referring to figures.

A semiconductor device having an ISB™ configuration described above willbe taken as an example for a following explanation of the preferredembodiment of the present invention. FIG. 4 shows a cross sectional viewof a semiconductor device according to the present embodiment. Thissemiconductor device includes a multilevel interconnect configuration,and the element 410 a and the circuit element 410 b that are formed onthe multilevel interconnect configuration. The multilevel interconnectconfiguration includes a plurality of interconnect layers stacked, eachof which consists of the interlayer dielectric film 405 or 406 and theinterconnect line 407 made of copper, and the solder resist layer 408formed as the top layer. The solder ball 420 is provided on the backsidesurface of the multilevel interconnect configuration. The element 410 aand the circuit element 410 b are molded by the mold resin 415.

The pad electrode 460 is electrically connected to the interconnect line407. The pad electrode 460 and the element 410 a are connected by thegold wire 470. The pad electrode 460 and the element 410 b are connectedby a flip chip method. The pad electrode 460 includes a copper film anda plasma-resistant protective film, which is made of a conductivematerial, formed on the copper film. The configuration of theplasma-resistant protective film will be described below.

The resin materials such as a melamine derivative such as BT resin, aliquid crystal polymer, an epoxy resin, a PPE resin, a polyimide resin,a fluorocarbon resin, a phenol resin and a thermosetting resin such as apolyamide bismaleimide can be selected for the solder resist layer 408,the interlayer dielectric film 405 and the mold resin 415 in FIG. 4,respectively. In particular, the liquid crystal polymer, the epoxy resinand the melamine derivative such as BT resin are preferably used sincethey have an excellent high-frequency property. Filler or additive maybe arbitrarily added to the resin.

Next, a manufacturing method of the semiconductor device shown in FIG. 4will be described in reference to FIGS. 5A to 7C. The via hole 404 isformed at a predetermined location on the metal foil 400, and theconductive film 402 is formed in the via hole 404 selectively as shownin FIG. 5A. More specifically, after coating the metal foil 400 by thephoto resist 401, the conductive film 402 is formed on an exposed partof the surface of the metal foil 400 by an electric field platingmethod. The conductive film 402 has a thickness of about 1 to 10 μm, forexample. Since the conductive film 402 will become finally a backsideelectrode of a semiconductor device, gold or silver, which has a goodadhesiveness for brazing filler metal such as solder, is preferably usedfor the conductive film 402.

After that, the interconnect pattern of the first layer are formed onthe metal foil 400 as shown in FIG. 5B. First, chemical polishing isperformed against the metal foil 400 for cleaning the surface and toform a rough surface. Next, the conductive film 402 on the metal foil400 is entirely coated by thermosetting resin, and heat hardening isperformed so that the film surface becomes flat. Next, a via hole with adiameter of about 100 μm reaching to the conductive film 402 is formedin the film. The via hole is formed by a laser processing in the presentembodiment. Machining, chemical etching, and dry etching by using plasmacan be also used to form the via hole. After that, etching residue isremoved by laser exposure, and a copper plating layer is formed onoverall the surface with embedding the via hole 404. The copper platinglayer is etched by using a photo resist mask so that the interconnectline 407 made of copper is formed. The interconnect pattern can beformed by removing unnecessary copper foil by spraying etching solutionto the surface exposed out of the resist, for example.

The formation of the interlayer dielectric film 405, the via hole andthe copper plating layer, and the patterning of the copper plating layermentioned above are repeated in turn so that the multilevel interconnectconfiguration in which the interconnect layers including theinterconnect line 407 and the interlayer dielectric films 405 and 406are stacked is formed as shown in FIG. 5C.

After the formation of the pad electrodes 460 and the solder resistlayer 408 that has openings at the locations of the pad electrodes 460,the element 410 a and the circuit element 410 b are formed on the solderresist layer 408. A dielectric material that has a good solder heatresistance is used for the solder resist layer 408. For example, anepoxy resin may be used. The element 410 a and the circuit element 410 bmay be, for example, semiconductor chips such as a transistor, a diodeand an IC chip, or passive elements such as a chip capacitor and a chipresistor. Face-down semiconductor elements such as a CSP and a BGA maybe also mounted. In the present embodiment, the element 410 a is a baresemiconductor chip (a transistor chip) and the circuit element 410 b isa chip capacitor. These elements are stuck on the solder resist layer408.

The formation process of the configuration shown in FIG. 6A is nowdescribed referring to FIG. 7. After formation of a copper film on theinterlayer dielectric film 406, the electrode film 462 is formed bypatterning processes. After that, the adhesive film 464 is formed on thesurface of the electrode film 462 by a selective plating method,followed by forming the coating film 466. Nickel, chrome, molybdenum,tungsten, aluminum or an alloy of them is, for example, used for theadhesive film 464. Gold, silver, platinum or an alloy of them is, forexample, used for the coating film 466. Each of the films may haveeither a single layer or a double layer. Next, the solder resist layer408 is formed by thermocompression of a solder resist sheet stuck on thesurface of the interlayer dielectric film 406. Opening is formed at thelocation of the electrode film 462 in the solder resist layer 408 byexposure and development. A void part is provided between the side wallof the electrode film 462 and the inside wall of the opening in thesolder resist layer 408. Although the solder resist layer 408 made of anepoxy resin is formed by using an epoxy resin sheet in the presentembodiment, other kinds of material may be used.

When the electrode film 462 is made of copper or copper-aluminum alloy,nickel and gold are, for example, preferably used for the adhesive film464 and the coating film 466, respectively. This combination is adoptedin the present embodiment.

The pad electrode 460 with a plasma-resistant protective film, in whichthe adhesive film 464 and the coating film 466 are stacked on theelectrode film 462 in this order, is formed as mentioned above. In thisconfiguration, the coating film 466 contributes to improvement ofplasma-resistance, and the adhesive film 464 contributes to improvementof the adhesion between the coating film 466 and the electrode film 462.The configuration shown in FIG. 6A can be obtained as described above.

Plasma treatment is performed for the configuration shown in FIG. 6A.The plasma exposure condition may be arbitrarily determinedcorresponding to used resin so that a cluster of micro projectionsmentioned above is formed. A bias voltage is preferably not applied tothe substrate. For example, the following condition is adopted.

-   -   Bias voltage: no voltage applied    -   Plasma gas: argon of 10 to 20 sccm and oxygen of 0 to 10 sccm

By the plasma exposure, the surface of the interconnect line 407 iscleaned, the surface property of the solder resist layer 408 ismodified, and a cluster of micro projections is formed on the surface.The cluster of micro projections formed on the surface of the solderresist layer 408 and the surface of the elements 410 a and 410 b have anaverage diameter of 1 to 10 nm and a number density of about 1×10³ μm⁻².

After connecting the element 410 a and the pad electrode 460 by the goldwire 470, they are molded by the mold resin 415 as shown in FIG. 6B.FIG. 6B shows a molded configuration. The mold process of semiconductorelements is performed simultaneously for a plurality of modules mountedon the metal foil 400 by using a mold. Transfer mold, injection mold,potting and dipping may be used for the mold process. When athermosetting resin such as an epoxy resin is used, the transfer mold orpotting can be adopted. When a thermoplastic resin such as a polyimideresin and a polyphenylene sulfide is used, the injection mold can beadopted.

After removing the metal foil 400 from the configuration shown in FIG.6B, solder balls are formed on the backside surface. The metal foil 400can be removed by polishing, grinding, etching or laser vaporization,for example. The method adopted in the present embodiment is as follows:the metal foil 400 is overall grinded about 50 pm by a polisher or agrinder, and the rest of the metal foil 400 is removed by chemical wetetching. Wet etching may be used also for removing the entire metal foil400. By these processes, the lower surface of the interconnect line 407in the first layer is exposed on the opposite side of the surface wherethe semiconductor elements are mounted. With this configuration, amodule having a flat underside surface is obtained in the presentembodiment. Therefore, when the semiconductor device is mounted, itmoves horizontally by surface tension of solder and so on, and anadvantage in the processing, i.e., easy self alignment, can be obtained.

After that, the solder ball 420 is formed by sticking a conductivematerial such as solder on the backside surface of the conductive film402, which is exposed by removing the metal foil 400. Then thesemiconductor device shown in FIG. 4 is obtained by dicing. The wafer issubsequently cut by dicing so that a chip of the semiconductor devicecan be obtained. The metal foil 400 is a supporting substrate beforeremoving the metal foil 400 as described above. The metal foil 400 isalso used as an electrode in the electric field plating process to formthe interconnect line 407. Furthermore, also when the mold resin 415 ismolded, the metal foil 400 makes the workability of carrying to a moldand of mounting in the mold favorable.

In the semiconductor according to the present embodiment, the propertyof surfaces of the solder resist layer 408, the element 410 a and thecircuit element 410 b is modified by Ar plasma treatment in the processshown in FIG. 6A, and micro projections are formed thereon. As a result,the interface adhesiveness between them and the mold resin 415 issignificantly improved, and the yield rate and the element reliabilityare advanced.

Moreover, a bad connection between a semiconductor chip and aninterconnect layer can be suppressed in the wire bonding process sincethe surface of the pad electrode 460 does not degrade even if such aplasma treatment as described above is performed. Therefore, highreliability and a high yield rate can be realized.

Although the present invention has been described by way of exemplaryembodiments, it should be understood that many changes and substitutionsmay be made by those skilled in the art without departing from thespirit and the scope of the present invention which is defined only bythe appended claims.

1. A semiconductor device comprising: a base material; a conductorcircuit in the base material; a dielectric film covering at least partof the base material; a pad electrode on a surface of the base materialor a surface of the dielectric film and connected with the conductorcircuit; a semiconductor chip on the dielectric film; a conductivemember electrically connecting the pad electrode and the semiconductorchip, wherein the pad electrode comprises an electrode film and aconductive protective film on a surface of the electrode film, whereinone end of the conductive member contacts the conductive protective filmand wherein the surface of the dielectric film is a plasma treatedsurface, and the surface of the conductive protective film comprises aplasma-resistant material.
 2. The semiconductor device of claim 1,wherein the conductive protective film comprises an adhesive film formedon the electrode film, and a coating film formed on the adhesive film,which constitutes the surface of the conductive protective film.
 3. Asemiconductor device comprising: a base material; a conductor circuitprovided in the base material; a dielectric film covering at least apart of the base material; a pad electrode provided on a surface of thebase material or a surface of the dielectric film and connected with theconductor circuit; a semiconductor chip formed on the dielectric film;and a conductive member electrically connecting the pad electrode andthe semiconductor chip, wherein the pad electrode comprises an electrodefilm and a conductive protective film formed on a surface of theelectrode film, the conductive member is formed so that one end thereofcontacts with the conductive protective film, and a cluster of microprojections is formed on the surface of the dielectric film.
 4. Thesemiconductor device of claim 1, wherein a cluster of micro projectionsis formed on the surface of the dielectric film.
 5. The semiconductordevice of claim 3, wherein the conductive protective film comprises anadhesive film formed on the electrode film, and a coating film formed onthe adhesive film, which constitutes the surface of the conductiveprotective film.
 6. The semiconductor device of claim 3, wherein thesurface of the dielectric film is a plasma treated surface and thesurface of the conductive protective film comprises a plasma-resistantmaterial.
 7. The semiconductor device of claim 3, wherein the dielectricfilm has a concave part, the pad electrode is formed inside the concavepart, and there is a gap between the inside wall of the concave part andthe side wall of the pad electrode.
 8. A semiconductor devicecomprising: a base material; a conductor circuit provided in the basematerial; a dielectric film covering at least a part of the basematerial; a pad electrode provided on a surface of the base material ora surface of the dielectric film and connected with the conductorcircuit; a semiconductor chip formed on the dielectric film; and aconductive member electrically connecting the pad electrode and thesemiconductor chip, wherein the pad electrode comprises an electrodefilm and a conductive protective film formed on a surface of theelectrode film, the conductive member is formed so that one end thereofcontacts with the conductive protective film, and the conductiveprotective film comprises an adhesive film formed on the electrode film,and a coating film formed on the adhesive film, which constitutes thesurface of the conductive protective film.
 9. The semiconductor deviceof claim 8, wherein the surface of the dielectric film is a plasmatreated surface and the surface of the conductive protective filmcomprises a plasma-resistant material.
 10. The semiconductor device ofclaim 8, wherein the dielectric film has a concave part, the padelectrode is formed inside the concave part, and there is a gap betweenthe inside wall of the concave part and the side wall of the padelectrode.
 11. The semiconductor device of claim 8, wherein a cluster ofmicro projections is formed on the surface of the dielectric film. 12.The semiconductor device of claim 8, wherein the adhesive film isselected from a group consisting of Ni, Cr, Mo, W and Al.
 13. Thesemiconductor device of claim 8, wherein the coating film is selectedfrom a group consisting of Au, Ag and Pt.